Such a control arrangement may be used in, for example, telephone stations having a loudspeaker and be arranged before the amplifier which feeds the loudspeaker. Whatever the level of the signal received in the control range, this control arrangement enables the amplifier to operate with a constant signal level at its input and to ensure a constant sound level, which is selected by the user by adjusting the gain of the amplifier.
The properties which such a control arrangement must satisfy are, particularly, a simple construction, low cost and the possibility of integration. In addition, this control arrangement must produce a signal which can be amplified in a simple way and with little cost in a loudspeaker amplifier which must also be integrable.
The known control arrangements are circuits denoted AGC (automatic gain control) in which the level of the voice signal received is detected for controlling an attenuation circuit of this received signal. A circuit of this type is used in, for example, the telephone station described in the article "Model S-1P Loudspeaker Telephone Circuit Design" by K. Kato et al., published in the periodical "Review of the Electrical Communication Laboratories", Volume 27, Nos. 5-6, May-June 1979, pages 347-367. In the solution proposed therein the signal which is applied to the loudspeaker amplifier has the shape of the voice signal, which makes this amplifier comparatively expensive to produce and it has a mediocre efficiency, which is not favourable for its integration.